1. Field of the Invention
The invention relates to power strips, and more particularly to multiple outlet power strips that are tamper-resistant so as to prevent children from injury.
2. Description of Related Art
Power strips are commonly employed electrical devices for enabling several appliances to be operated from a single power source. A common power strip has a plug, for plugging into the power source, and multiple outlets. The plugs from each of the appliances are inserted into the outlets of the power strip and all can be used simultaneously.
Surge protectors or suppressors are common electrical devices which prevent sensitive electrical appliances and equipment (such as computers and audio systems) from being harmed by sudden spikes in voltage. A voltage surge is typically considered to be a transient wave of voltage on the power line, having an amplitude of up to several thousand volts and a duration of between 1-100 milliseconds. Common effects of voltage spikes are damage to electronic components and/or loss of data and programs in computer memories. Voltage spikes can be caused by a number of events, such as lightning striking power lines, switching of transmission lines by electrical utilities, or rapid connections or disconnections of large loads on the same line. The surge protector acts as a buffer and limits the peak voltage applied to an electronic device to a level which will not harm the device. Surge protectors typically employ a clipping circuit for this purpose.
The physical structure of a surge protector typically includes a non-conductive housing having a number of electrical sockets formed therein. The sockets typically are linked by common conductors and are formed in a row. The most common type of surge protector includes one row of sockets and is sometimes referred to as a power strip.
In households having small children, electrical outlets are commonly childproofed for safety reasons. If an electrical outlet is left exposed, small children are able to inadvertently or intentionally insert electrically conductive objects into the outlet. Such action may have a deleterious effect on both the children and the electrical system of the house; the electrical system may short out, and the children may be injured or electrocuted.
Typically, a plastic plug is inserted into an outlet to childproof it. This prevents the insertion of another object. However, when it is desired to use the outlet, the plastic plug must be removed. It is not uncommon to lose the plug during the use of the outlet and then not be able to replace the plug in the outlet afterwards.
Electrical outlets have been developed that have child safety features integrally formed therein. One common design includes a cap which is pivotally mounted on top of the outlet. In order to use the outlet, the cap must be flipped up to expose the socket. Another common design entails placing a rotatable nonconductive plate over the socket. The plate has holes which correspond to the socket. However when the outlet is not in use, the plate is biased in a position where the holes in the plate do not align with the holes of the socket. When it is desired to use the outlet, the plate is rotated or slid so as to align the plate holes with the outlet holes. Typically, the plate is mounted to the socket and biased with a torsion spring. Such an arrangement is depicted in, for example, U.S. Pat. Nos. 2,154,160 to Hamilton and 2,752,581 to Benander. Use of torsion springs is not, however, a perfect solution, as they are prone to break.
Another childproof outlet is described in U.S. Pat. No. 4,584,430 to Belknap. Belknap describes a plate mounted in front of a socket having radially extending arms disposed on opposing sides of the plate. Nonconductive linearly resilient bands such as rubber bands are attached to these arms and also attached to fixed points on the housing. The rubber bands bias the plate in a position where the holes of the plate are not aligned with the holes of the socket. This outlet suffers from the deficiency that rubber bands are prone to become brittle with age and use.
A similar outlet is described in U.S. Pat. No. 2,524,250 to Bierce. In this reference, a plate is rotatably mounted in front of a socket and is provided with holes corresponding to the holes in the socket. A coil spring biases the plate in a position where the holes of the plate are not aligned with the holes of the socket. The spring is disposed in an arcuate slot and is bent in an arcuate fashion alone the slot. Such non-linear deformation is conducive to shortening the life-span of the spring.
Most of the above outlets are designed for two-pronged plugs. Only Belknap illustrates a third ground hole to accommodate three-prong plugs. The standard three-prong plug possesses a ground plug that is substantially longer than the other two plugs. The preferred method of turning the childproofing plate out of the way so that its holes align with the holes of the socket is to insert a plug into the holes of the plate and turn the plate by hand. However, since the ground prong of the three-prong plug is substantially longer than the other two prongs, it is difficult to insert all three prongs into the holes of a plate such as that described in Belknap; the ground prong will enter the ground hole, but the other two prongs will be too short to enter their respective holes. As a result, the plate must be turned by another more cumbersome means, such as by use of fingers alone. Depending on the strength of the biasing means, this procedure can be very difficult.